1. Field of the Invention
The present invention relates to a backlight system and related method, and more particularly, to a backlight system and related method based on a lamp current balance and feedback mechanism.
2. Description of the Prior Art
Because liquid crystal display (LCD) devices are characterized by thin appearance, low power consumption, and low radiation, LCD devices have been widely applied in various electronic products such as computer monitors, mobile phones, personal digital assistants (PDAs), or flat panel televisions. In general, the LCD device comprises liquid crystal layers encapsulated by two substrates and a backlight system for providing a light source. The operation of an LCD device is featured by varying voltage drops between opposite sides of the liquid crystal layers for twisting the angles of the liquid crystal molecules of the liquid crystal layers so that the transparency of the liquid crystal layers can be controlled for illustrating images with the aid of the backlight system.
The backlight system of an LCD device is normally disposed at the lower or lateral sides of the LCD panel of the LCD device. The backlight system in conjunction with various optical devices (such as diffusers and prisms) is able to provide a high-intensity and uniform light source for the LCD panel. That is, based on the voltage drops between opposite sides of the liquid crystal layers of the LCD panel with the aid of the uniform light source, the luminance and chromaticity of panel pixels can be controlled precisely so that the LCD device is capable of displaying high-quality images.
Please refer to FIG. 1, which is a structural diagram schematically showing a prior-art backlight system. As shown in FIG. 1, the backlight system 100 comprises a driving circuit 160, a transformer 120, a capacitor 180, and a lamp 140. The lamp 140 of the backlight system 100 is driven based on single-side driving mode. The transformer 120 comprises a first winding (primary winding) 121 and a second winding (secondary winding) 122. The driving circuit 160 is utilized to provide an AC driving voltage to the first winding 121 of the transformer 120. The second winding 122 of the transformer 120 in conjunction with the capacitor 180 performs a resonant operation for generating an AC voltage Vx having a high peak-to-peak voltage. The AC voltage Vx is then utilized to drive the lamp 140 for lighting. It is well-known that the length of the lamp 140 is increased with the panel size of liquid crystal display devices, and the peak-to-peak voltage of the AC voltage Vx should be also increased for driving the lamp 140 having greater length. Consequently, the current leakage of the lamp 140 becomes more serious resulting from the greater AC voltage Vx. Furthermore, the capacitor 180 and the transformer 120 are a costly high-voltage capacitor and a costly high-voltage transformer respectively for providing the greater AC voltage Vx. In view of the aforementioned shortcomings concerning the prior-art backlight system 100, it is obvious that backlight systems based on single-side driving mode cannot meet future demands for LCD devices having large panel size.
Please refer to FIG. 2, which is a structural diagram schematically showing another prior-art backlight system. As shown in FIG. 2, the backlight system 200 comprises a first driving circuit 260a, a second driving circuit 260b, a first transformer 220a, a second transformer 220b, a first capacitor 280a, a second capacitor 280b, and a lamp 240. The lamp 240 of backlight system 200 is driven based on double-side driving mode. The first driving circuit 260a is utilized to provide a first AC driving voltage to the first winding 221 of the first transformer 220a. The second driving circuit 260b is utilized to provide a second AC driving voltage to the first winding 223 of the second transformer 220b. The second winding 222 of the first transformer 220a in conjunction with the first capacitor 280a performs a resonant operation for generating a first AC voltage Va having a high peak-to-peak voltage. The second winding 224 of the second transformer 220b in conjunction with the second capacitor 280b performs a resonant operation for generating a second AC voltage Vb having a high peak-to-peak voltage. Therefore, both the first capacitor 280a and the second capacitor 280b should be costly high-voltage capacitors. The first AC voltage Va is furnished to the first end of the lamp 240. The second AC voltage Vb having opposite phase relative to the first AC voltage Va is furnished to the second end of the lamp 240. That is, the lamp 240 is driven based on the first AC voltage Va and the second AC voltage Vb having phase opposite to each other.
Due to production inaccuracy, aging or other factors, parameter discrepancy may occur to different elements, such as the capacitance deviation between the first capacitor 280a and the second capacitor 280b or the winding deviation between the first transformer 220a and the second transformer 220b, and therefore the currents furnished to the first and second ends of the lamp 240 may not have same current value. In addition, the current leakage of the lamp 240 is likely to occur under high-voltage operation because of parasitic capacitors corresponding to the lamp 240 regardless of the lamp 240 being a cold-cathode fluorescent lamp (CCFL) or an external electrode fluorescent lamp (EEFL). Consequently, the current inconsistency at the first and second ends of the lamp 240 is likely to occur in the operation of the backlight system 200. That is, the lamp 240 of the backlight system 200 is not able to generate uniform light output, and therefore display panels using the backlight system 200 cannot display images accurately.